Pipelines used to transport oil and gas are often subject to corrosion as a result of various components found in the oil and gas. One type of corrosion is referred to as top-of-line corrosion and is caused when liquids, in particular water, condense on the top inner surface of the pipeline. This occurs when a pipeline is operated with a combined gas/liquid flow such that the liquid portion of the flow only contacts a portion of the inner surface of the pipeline. The corrosion is often a result of contaminants in the gas such as carbon dioxide, hydrogen sulfide and/or organic acids, and water condensation as a result of pressure and temperature changes in the pipeline.
Corrosion inhibitors are often injected into the pipeline with the oil and gas to prevent corrosion, but when the pipeline is not operated liquid full the corrosion inhibitor does not come into contact with the top inner surface of the pipeline. As a result, there is not an effective way to treat the top inner surface of the pipeline with corrosion inhibitors. This condensation is especially prevalent in the portion of the pipeline near the wellhead where the oil and gas cools as it leaves the well.
Conventional pigs similar to those disclosed in U.S. Pat. No. 5,903,946 can be used for cleaning the interior of pipes as the pig is moved in an axial direction through the pipe. Even when pigging a pipeline though, the pipeline is typically not liquid full, and there is no way to guarantee that injecting corrosion inhibitors during a pigging operation will result in full contact between the corrosion inhibitor and the top inner surface of the pipeline.